Printing of timing marks in the xerographic process



Dec. 23; 1969 B. c@ SEW'ELL PRINTING OF TIMING MARKS INIYTHEXEROGRAPHIC PROCESS Filed Sept. 1, 1966 INVENTOR. BRIAN C. SEWELL 7 9 WM A TTORNEYS United States Patent 3,485,622 PRINTING OF TIMING MARKS IN THE XEROGRAPHIC PROCESS Brian Constantine Sewell, Teddington, England, assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed Sept. 1, 1966, Ser. No. 576,576 Int. Cl. G03g 13/00 US. Cl. 96-1 3 Claims ABSTRACT OF THE DISCLOSURE A positive to positive xerographic process for imaging, timing marks on a moving xerographic surface by uniformly charging the surface and then exposing the surface through a mask positioned between a light source and the surface, the mask having an opaque area in configuration of the mark to be produced and a transparent area surrounding mark which tapers ofi? into opaque areas on the edges of the mask.

This invention relates in general to the production of timing marks on the surface of a xerographic member and in particular to the production of timing marks in a positive-to-positive mode of operation of a xerographic apparatus.

More specifically, the invention relates to the production of timing marks by the use of electrostatic charge developed on the surface of a xerographic drum. Timing marks are used in the copying art to actuate subsequent apparatus in timed relation to the position of reproduced material. For example, timing marks are positioned on a web of paper or the like to indicate the leading and trailing edge of copy being reproduced on the web. The marks are subsequently used to actuate paper cutters to sever the web at the leading and trailing edge of the copy being reproduced. Timing marks may be used for any other purpose which is desired but in most cases they are sensed or detected and used to actuate some subsequent piece of equipment.

In the normal operation of the xerographic process, a uniform electrostatic charge is applied to a photoconductive surface and the surface is exposed to a light image of the copy being reproduced. The light image normally is in the form of a positive image, i.e., a dark image on a light background. Therefore, the light from the nonimage areas strikes the xerographic surface and renders the surface conductive dissipating thecharge thereon. Electrostatic charge remains on the xerographic surface in the image areas, that is, in the areas which were not exposed to light and the image is developed with a powder which has a triboelectric charge at opposite polarity to the charge on the surface and is thereby attracted to the image areas. This is a positive type of reproduction as that term i used herein. Negative reproduction, as used herein, is where light reaches the uniformly charged photoconductive surface in the image areas thus discharging the electrostatic charge in the image areas.

In the xerographic process when the image developed on the xerographic drum is a positive image, as is normally the case, there is a problem of producing a timing mark with the electrostatic charges on the drum surface. It would be desirable to be able to uniformly charge the surface of the xerographic drum including the area which will contain the timing mark and to be able to produce the timing mark merely by flashing a light. If this were done through an opaque mask with a transparent bar or mark, the charge in the area of the mark would be dissipated and the remainder of the surface of the drum 3,485,622 Patented Dec. 23, 1969 "ice would have a uniform electrostatic charge thereon. Then in the production of copy on the surface of the drum, the mark would be indicated by an undeveloped spot. In order to develop this mark, a powder or toner would be necessary which has a triboelectric charge that is the same as the charge on the plate and thus be attracted to the uncharged image areas. This would be a different toner than that used to develop the copy being reproduced thus requiring a separate development system to develop the timing mark. If the mask used were transparent and the bar or mark opaque, then when a light is flashed the drum would be discharged in the area of the mask except for the bar or mark. In this case, with the production of positive copy, the mark would be developed on the drum and the surrounding areas would be undeveloped. This is the situation that is desirable, however, since the light is not on constantly there would be areas where there were to be no mark that would have charge remaining on the drum surface and thus would have developed areas which would be subsequently sensed as a mark. If the light were left continually illuminated to discharge these areas, then the areas that were to have a mark would also be exposed after they passed the mask and no mark would be developed. The negative reproduction would be where a neative and photographic film is used and light reaches the uniformly charged photoconductive surface in the image areas only thus discharging the electrostatic charge in the image areas.

It is therefore the primary object of this invention to produce timing marks on a xerographic surface by the actuation of a light source.

It is a further object of this invention to produce timing marks on a xerographic surface in the production of positive copy.

It is a still further object of this invention to produce timing marks on a xerographic surface without dissipating the entire electrostatic charge in the background areas.

These and other objects of this invention are obtained by exposing the drum surface through a mask positioned between a light source and the surface of a xerographic drum, the mask having an opaque area in configuration of the mark to be produced and a transparent area surrounding the mark which tapers or gradually blends off into opaque areas on the edges of the mask.

For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic View of apparatus embodying the present invention.

FIG. 2 is an isometric view of a mask suitable for use in the present invention.

The position of timing marks is usually just adjacent to the printed material on which they appear and may be produced by such means as a graphite marker or, in Xerography, by producing an electrostatic image of the mark and developing the image with xerographic toners. The present invention pertains to the production of the latter type of mark.

The development of the electrostatic image occurs at the boundaries between areas having electrostatic charge and areas having no electrostatic charge. That is, development occurs at points where there are sharp potential differences. Areas which are uniformly charged do not have a field created which is sufficient to attract the toner material, thus the larger solid areas remain undeveloped unless the charge pattern in these areas is broken up. A theoretical discussion of the development of solid areas is found in the book Xerography and Related Processes by Drs. Dessauer and Clark, chapters 8 and 9, published by the Focal Press of London and New York. The characteristic of Xerography wherein development occurs only at edge portions or charge gradients of images which are large compared to the thickness of the photoconductive film is utilized in the present invention. That is, the failure of areas which do not have sharp steps or gradients in potential to develop is essential to the operation of the present invention.

If the timing marks are to be produced xerographically in a positive-to-positive mode operation, that is, an image is being reproduced xerographically from a photographically positive original and a photographically positive copy is to be produced, then the timing marks should be dark sharp images on a clear or undeveloped background. To produce a clear sharp mark, an electrostatic image must be produced on the photoconductive surface which has sharp gradient potentials only at the edges of the mark to be produced.

In xerographic reproduction a photoconductive surface or drum, as drum 10 in FIG. 1, is uniformly electrostatically charged over its surface with a corotron 11. The area in which timing marks are to be produced is indicated as 12 and is usually a strip along the margin of the copy to be reproduced. This strip 12 is also uniformly charged at the same time as the remainder of the Xerographic surface.

The surface of the xerographic photoconductive member is constructed of amorphous selenium or other photoconductive material. There is a lamp or discharged tube 18, an optical condenser lens 22, a projection lens 24, and a film or mask 20, all positioned adjacent to the edge of xerographic drum 10 above strip 12. The lamp 18 is adapted to be pulsed to produce the timing marks in response to predetermined signals and in time relation to the rotation of the xerographic drum.

The drum 10 would normally be associated with all 4 the boundary of the transparent and opaque areas, the transparent area is very gradually darkened or blended into the opaque area so that there is no definable boundary between the discharged and undischarged portions on the xerographic drum. Therefore, with no sharp or definable changes in potential except around the edge of the opaque mark, there will be no halo effect produced. The areas of the drum which are fully charged will not be developed and the transparent areas will not be developed because there is no charge remaining in those areas. Between the transparent and the opaque area, the charge will be discharged uniformly without any sharp potential gradients thus this area will also fail to be developed. This arrangement results in sharply defined opaque marks developed pertinent xerographic stations; for example, a corotron or line or mark 26 in the center thereof. Surrounding the opaque mark is a transparent area which gradually fades into an opaque area round the outer edge portion of the film. If the transparent area terminated sharply in an opaque area around the edge of the film, then the image produced on the drum when the lamp is flashed would contain sharp changes in potential at both edges of the opaque mark and at the points where the transparent area and the opaque areas met. Thus, during development toner powder would adhere to the electric field created between the opaque area and the transparent area ahead of the opaque mark and at the boundary of the opaque area and the transparent area after the mark thereby producing developed marks which would be sensed in the same manner as the timing mark. The timing mark would appear as a clear distinct mark on the final copy but having a halo surrounding it.

In order to eliminate the halo effect or development at on the surface of the xerographic drum and transferable to the final web or copy sheet. The transparent and translucent areas should be kept as small as possible so that sharply defined marks may be spaced as closely adjacent as possible.

While the invention has been described with reference to the structure disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.

What is claimed is:

1. A positive-to-positive Xerographic process for forming timing marks comprising the steps of uniformly charging the surface of a xerographic radiation sensitive member and exposing a confined area of said surface through a mask having an opaque area in the configuration of the mark to be produced and a transparent area surrounding the mark which tapers off into opaque areas on the edges of the mask.

2. The process of claim 1 wherein a timing mark may be recorded in any of a series of non-overlapping confined areas.

3. A method of producing timing marks on a Xerographic member by exposing a confined area of an electrostatically charged xerographic member to an image of an opaque mark surrounded by a transparent area which gradually fades into an opaque area, and developing the member, after exposure, with finely divided electrostatically attractable powder.

References Cited UNITED STATES PATENTS 3,105,425 10/1963 Cerasoni et al l.7

3,135,180 6/1964 Cerasoni et al. 95-1.7

3,244,084 4/1966 Darus 951.7

FOREIGN PATENTS 1,777,487 9/ 1964 Germany.

GEORGE F. LESMES, Primary Examiner JOHN C. COOPER III, Assistant Examiner US. Cl. X.R. 

